Hard tissues

Enamel

Hardest tissue; 97% hydroxyapatite; ectoderm-derived; acellular.

Ameloblasts

Ectodermal cells that secrete enamel and pull away.

Dentin

Second hardest tissue; 75% hydroxyapatite, 25% collagen; tubular structure.

Odontoblasts

Dermis/neural crest cells that produce dentin and retreat.

Dentinal Tubules

Microscopic tubes giving dentin strength and nerve sensitivity.

Scrimshaw

Artifacts carved from whale teeth or walrus tusks; pure dentin with no enamel.

Hydroxyapatite

Calcium phosphate mineral providing hardness to skeletal tissues.

Bone Composition

70% hydroxyapatite (mineral) and 30% collagen fibers (organic).

Antler Bone

Only 50% hydroxyapatite; more flexible to prevent breaking during fights.

Whale Tympanic Bulla

86% hydroxyapatite; dense for underwater sound transmission.

Osteoblasts

Bone-forming cells that secrete bone matrix around themselves.

Osteocytes

Mature bone cells trapped inside lacunae.

Osteoclasts

Bone-resorbing cells that break down bone matrix.

Lacunae

Cavities within matrix housing osteocytes or chondrocytes.

Canaliculi

Microscopic canals linking lacunae for nutrient/waste transport.

Osteon

Concentric lamellae surrounding a central neurovascular canal.

Cortical Bone

Compact, dense outer bone made of tightly packed osteons.

Trabecular Bone

Spongy internal bone made of branching struts (trabeculae).

Red Bone Marrow

Cellular marrow producing blood cells and osteoblasts.

Yellow Bone Marrow

Fatty, adipose-rich bone marrow.

Dermal Bone

Bone formed directly in dermis without a cartilage precursor (e.g., skull roof, clavicle).

Endochondral Bone

Bone that replaces an embryonic hyaline cartilage model (e.g., long bones).

Diaphysis

Shaft of a long bone; primary ossification center.

Epiphysis

End cap of a long bone; secondary ossification center.

Epiphyseal Plate

Cartilage growth plate between diaphysis and epiphysis; ossifies to stop growth.

Anosteocytic Bone

Acellular bone lacking osteocytes; found in advanced bony fish.

Orthodontic Movement

Compression side: osteoclasts erode bone. Tension side: osteoblasts build bone.

Chondroblasts

Cells that secrete cartilage matrix.

Chondrocytes

Mature cartilage cells trapped in lacunae.

Cartilage Matrix

Avascular, non-mineralized matrix of chondroitin sulfate and high water.

Hyaline Cartilage

Smooth, glassy, low-fiber cartilage (e.g., joint surfaces, growth plates, shark rostrum).